My Audatron SH-608Rs have had damping and earpad modifications. The drivers were also lifted off the baffle and suspended away from the ear.
-- Opened up soundstage, made sound airy and light
-- Fixed boomy and peaky mids
-- Sound is no longer suffocating and oxygen-deprived
-- Still sounds bad :(

My KOSS Pro/4AAA has had damping modifications. I also cut holes in the earcups to make it open-backed, gave it new pads, completely rewired it and added 3.5mm detachable cables to each side.
--Removed an annoying echo that was interfering with the soundstage
--Evened out the frequency response
--Removed a slight bloom on the low end
--Possibly a slight increase in treble